A specific example of a conventional LSI package structure is shown in FIG. 1.
In FIG. 1, a plurality of LSIs 56 are loaded on the upper surface of a common ceramic substrate 55, and a plurality of pins 57 are protruded on the lower surface of the substrate 55. These pins 57 comprise a signal input/output terminal, a power supply terminal and a ground terminal for the LSI 56. Thus, an LSI package 50 is constituted. The LSI package is described in, for example, "IEICE TRANSACTIONS, VOL. E74, NO. 8, AUGUST 1991, PP 2331-3336".
The LSI package 50 is packaged on a multilayer printed interconnection board 51 by using a multipolar connector 52. To the multipolar connector 52, a plurality of sockets 53 which are each fitted with the pin 57 of the LSI package 50 are provided, and lead pins 54A through 54C extending downwardly are each connected to the socket 53. The foregoing pins 57 are each inserted through the socket 53 to achieve electrical and mechanical connection between the LSI package 50 and the multipolar connector 52. The printed interconnection board 51 comprises a power supply pattern layer 61, a signal pattern layer 62 and a ground pattern layer 63 and, further, a through hole 64 at an appropriate position. The foregoing pattern layers 61 through 63 are each made through by any of the through holes 64. The foregoing lead pins 54A through 54C are inserted through the through hole 64 to thereby achieve electrical and mechanical connection between the multipolar connector 52 and the printed interconnection board 51. Here the lead pin 54A is connected to the power supply pattern layer 61 connected to the power source, the lead pin 54B to the ground pattern layer 63 and the lead pin 54C to the signal pattern layer 62, respectively. Further, to the lead pin 54C, a cable connector 58 is connected for the input/output of the signal from and to the exterior.
In the package structure arranged as above, power supply to the LSI 56 is achieved from the power supply pattern layer 61 and the ground pattern layer 63 of the printed interconnection board 51 through the lead pins 54A, 54B and the socket 53 and the pin 57. Further, input and output of the signal to and from each LSI are achieved through the pin 57, socket 53, signal pattern layer 62 of the printed interconnection layer 51 and the cable connector 58.
Incidentally, recently, as the LSI loaded on the LSI package is highly integrated, its power consumption also tends to increase. In consequence, in the power supply system according to the foregoing conventional package structure, a need arises to increase the number of the power supply pattern layer 61 and the ground pattern layer 63 of the printed interconnection board 51, and the aspect ratio (board thickness/through hole diameter) is increased to make it difficult to manufacture the printed interconnection board. Further, since the current passes through the printed interconnection board 51, socket 53 and pin 57 over a long distance, the voltage drop can be increased. Still further, in terms of signal transmission, the transmission line is made very longer because it comprises the pin 57, socket 53, lead pin 54C and the cable connector 58, while it passes through the multipolar connector 52, which causes impedance discontinuity resulting in reduction of the transmission speed of the signal.